unit Unit17;

interface uses
   System.SysUtils, System.Classes,
   Winapi.Windows,
   Vcl.Controls, Vcl.Forms, Vcl.StdCtrls, Vcl.ComCtrls;

type
   TMyThread = class(TThread)
      protected var
         progressbarHandle: THandle;
      protected
         procedure Execute(); override;
      public
         constructor Create(const progressbarHandle: THandle);
    end;

   TForm1 = class(TForm)
      ProgressBar1: TProgressBar;
      Button1: TButton;
      procedure Button1Click(Sender: TObject);
   end;

var
   Form1: TForm1;

implementation uses Winapi.CommCtrl;

{$R *.dfm}

{ TMyThread }

constructor TMyThread.Create(const progressbarHandle: THandle);
begin
   inherited Create(True);
   self.progressbarHandle := progressbarHandle;
end;

procedure TMyThread.Execute();
var
   percentDone: Integer;
begin
   percentDone := 0;

   while (not Terminated) do
      begin
         Inc(percentDone, 1);

         PostMessage(progressbarHandle, PBM_SETPOS, percentDone, 0);
         if (percentDone < 100) then
            TThread.Sleep(100)
         else
            Terminate();
      end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
   myThread: TMyThread;
begin
   myThread := TMyThread.Create(ProgressBar1.Handle);
   myThread.FreeOnTerminate := True;
   myThread.Start();
end;

end.